1. Field of the Invention
The present invention relates to a power supply circuit comprising a line voltage forming circuit to be coupled to a telecommunication line having a line voltage for providing a supply voltage.
The present invention also relates to a telecommunication device comprising such a power supply circuit.
2. Description of the Related Art
Furthermore the present invention concerns a method for deriving a supply voltage from a telecommunication line voltage.
Such a power supply circuit, telecommunication device and method are being applied in telecommunication, in particular telephone ICs' wired or wireless subscriber telephones, a facsimile, a Web-television having a telephone card, a personal computer having a telephone card etc. These are known from Philips Semi-conductors Application Note AN 94069. The power supply IC described therein provides for facilities of a telephone subscriber set, such as handsfree facilities, listening-in facilities, dialling features, loudspeaker features etc. The stabilised power for these facilities is being supplied by and derived from the telecommunication line voltage. However the behaviour of the line power extracted from the telecommunication line is prescribed by the national telecommunication authorities, such as the PTT in the Netherlands. Within the line voltage versus line current characteristic the DC load line is precisely defined to lie in between forbidden area's. The growth of the features however, poses increasing demands on the maximum supply voltage which is necessary for these features to function optimally.